1. Field of the Invention
This invention relates to a method and apparatus for drawing a plurality of filaments bound with an armoring material in the shape of a band, and thereby providing a plurality of leaner filaments, both efficiently and economically.
2. Description of the Prior Art
Some of the methods of obtaining from filaments of a given diameter those of a smaller diameter are mentioned herein. One is termed "single head wire drawing," wherein filaments of a given diameter are passed through a single die one by one to form filaments of a smaller diameter. Another method is called "continuous wire drawing," wherein an apparatus comprising a plurality of dies and capstans corresponding in number to such dies is utilized. Another method involves inserting a filament of a given diameter into a tubular body having a caliber conforming to the diameter of the filament to form an integrated double structure, which is then drawn; and a plurality of said double structures are inserted into a tubular body of a greater caliber to be drawn as in the foregoing, and thereafter the processes of insertion into said tubular body and drawing are repeated.
In the first two methods, drawing is effected after inserting one wire into one die. Consequently, not only a bulky device is required for mass production, but also such methods are unsuitable for obtaining the so-called "filaments" having minute diameters. There is a further disadvantage, characteristic of wire drawing machining in general, that the machining speeds are extremely low.
It is only natural that the last of the above-mentioned three methods is considered the most suited for filament molding and, in fact, is adopted for practical use to prove its efficiency to a certain extent. This method has disadvantages too. First, technical difficulties are inevitable in a process of inserting a wire material of a great length into an elongated tube having a caliber conforming to the peripheral shape of the wire material for integration. Secondly, as in the first two methods, a process of drawing a wire (of a double structure in this case) through one die is of utmost importance, entailing great technical difficulties yet unsolved in the case of mass production. Thirdly, in this method, the filament obtained is of complex, multiple layers, with the armoring tubular bodies succeedingly enveloping an inner one from the outside according to the number of times of wire drawing. The volume of the tubular bodies at the armoring removing step in the last process is too great as compared with the total volume of the filaments, with resultant waste in time and labor required for armor removal, and high cost needed for the armoring tubular bodies. This method is, therefore, by no means a money-saving one.